1. Technical Field
The present invention relates to an electrophoretic display device and an electronic apparatus.
2. Related Art
A display device using electrophoresis (electrophoretic display device) is known. An electrophoretic display device has an electrophoretic layer between two substrates facing each other (in this specification, these two substrates are referred to as “pixel substrate” and “opposite substrate”), and performs display by utilizing the motion, under the influence of an electric field, of charged particles (migration particles) that migrate in a dispersion medium (solvent) that exists in the electrophoretic layer. The electric field is generated by applying a potential difference between the two substrates. A surface of one of the two substrates (surface of the opposite substrate) is a display surface. A partitioning wall is provided between the two substrates. The electrophoretic layer is compartmentalized by the partitioning wall into plural areas (cells). Each area (cell) constitutes, for example, a pixel. An electrophoretic display device can be applied to an electronic apparatus such as electronic paper. The abbreviated name of an electrophoretic display device is EPD (Electrophoretic Display).
In a production process of the display panel of an electrophoretic display device, for example, a partitioning wall unit for retaining dispersion liquid of an electrophoretic layer is formed on a pixel substrate unit that has a control circuit. Then, the dispersion liquid is poured into it. After that, the dispersion liquid is sealed by bonding a glass substrate (opposite substrate) that has a transparent electrode (common electrode) thereto. In such an electrophoretic display device, the control circuit of the pixel substrate unit controls potential between pixel electrodes, which are on the pixel substrate unit, and a common electrode. The content of display is controlled as a result of potential control therebetween.
FIG. 13 is a diagram that illustrates the contact structure 1011 of a COM electrode portion 1023 of an electrophoretic display device according to related art. The pixel area portion 1021 of a pixel substrate (backplane substrate), plural terminals whose number is M (where M is an integer greater than one; denoted as 1022-1 to 1022-M), a wiring line 1024, and the COM electrode portion 1023 are shown in FIG. 13. One terminal 1022-1 is connected to the COM electrode portion 1023 via the wiring line 1024. The COM electrode portion 1023 is connected to the common electrode of the opposite substrate (not illustrated in FIG. 13). As described above, the contact structure 1011 of the example illustrated in FIG. 13 has a portion for contact of the terminal 1022-1 and the COM electrode portion 1023 with each other (contact portion) in a part of the display panel.
In an electrophoretic display device, the height of an opposite substrate is approximately 500 [μm], and the height of partitioning wall is approximately 30 [μm]. Therefore, it would be difficult in terms of manufacturing cost to use a method of, as in a conventional semiconductor process, forming a through hole by etching and then sputtering metal such as AL (aluminum) for forming a contact for a common electrode. For this reason, it is common to form a contact for a common electrode by using conductive paste such as Ag (silver) paste.
FIG. 14 is a diagram that illustrates an equivalent circuit of the contact structure 1011 of the COM electrode portion 1023 of an electrophoretic display device according to related art. The schematic circuit configuration illustrated therein will now be explained. In the equivalent circuit, a COM electrode 1101 that is at a predetermined potential (VCOM0) is connected to a contact resistor (contact resistance) 1103 via a wiring line 1102. A point P1 is connected to one terminal of the contact resistor 1103. A point P2 is connected to the other terminal of the contact resistor 1103. A wiring line portion going through the contact resistor 1103 and another wiring line portion on which no circuit element is provided are connected in parallel between the points P1 and P2. The COM electrode 1101 of the predetermined potential (VCOM0) corresponds to the COM electrode of the COM electrode portion 1023 illustrated in FIG. 13. In the contact structure 1011 described above, it is not possible to directly measure the resistance value of the contact resistor 1103 of the COM electrode portion 1023.
With reference to JP-A-2009-115686, an example is shown below. A display device is disclosed in JP-A-2009-115686. In the display device, a conducting member is provided between a common electrode and a common electrode conducting portion (COM) (refer to FIG. 5 of JP-A-2009-115686). In this structure, when a display panel is driven, a voltage is applied to the common electrode conducting portion (COM) formed on the lower substrate. As a result, the voltage is applied via the conducting member to the common electrode. In this structure, it is not possible to directly measure the resistance value of the contact resistor of the common electrode.
As explained above, in an electrophoretic display device according to related art, it is not possible to directly measure the resistance value of the contact resistor of a common electrode. However, since an image is controlled in an electrophoretic display device by controlling an electric field between pixel electrodes and a common electrode, the resistance value of the contact resistor is an important parameter. For this reason, in some cases, it is necessary to measure the resistance value of the contact resistor. For example, in related art, there is a problem that a direct measurement approach cannot be taken; specifically, there is no option but to shave the periphery of a part of the common electrode so as to expose the contact portion of the common electrode, wire the exposed portion, and measure the resistance value of the contact resistor on the basis of the current value of the wiring indirectly. When production stability in mass production is considered, a structure that makes it possible to measure the resistance value of the contact resistor easily is very important.